The drilling and production of oilwells require the use of various different tubular goods; such as casing, tubing, subs, stabilizers, guns, and fishing tools; all of which are provided with threaded fastener means. Some of these joints of fluid conductors are provided with both a box end and a pin end, that is, a female and a male threaded surface located at the opposed marginal ends of the joint. The box end has an internal threaded surface which commences at a shoulder at one end of the joint and terminates in a vanish point. The pin end has an external threaded surface located between a vanish point and the other terminal end of the joint, so that when the pin end of one joint threadedly makes up respective to the box end of another joint, the two threaded members engage one another with great force or friction, thereby precluding one member inadvertently being unscrewed from the other.
The threaded ends of joints associated with boreholes have been standardized so that any stabilizer, for example, can be attached to any appropriate size sub, and the entire apparatus series connected within a string. The string likewise is made up of threaded joints, each of which have a box and a pin end, so that any of the above mentioned members can easily be incorporated into most any string.
Oilfield threaded joints are expensive, and from time to time the threaded surfaces thereof become unduly worn, and therefore, in order to economize, the threaded surfaces must occasionally be renewed by reforming the threads at the box and pin ends. This always shortens the joint a small amount. When the new threaded surface is formed on the joint, the joint usually is placed in an engine lathe, and special cutting tools are then employed to reform the opposed threaded ends of the joint, and then a thread gauge having threads thereon made complementary respective to the box and pin ends is threadedly made up with respect to the newly formed threaded surface. The machinist usually engages the lathe motor so that the joint is slowly turned while the prior art gauge threadedly makes up until the shoulder of the gauge abuttingly engages the new shoulder of the threaded member. Usually the gauge must be "tried" several times, with the threaded surface being progressively, slightly recut, depending upon the tightness or error of the new threads. Hence, the present art requires that the threads of the new pin or box end is gauged by trial and error, and therefore, the efficiency of the new threads is largely dependent upon the skill of the machinist.
As the prior art gauge is held stationary and the joint turned in order to threadedly make up with the gauge, sometime the tool will prematurely make up, causing the gauge device to rotate with the joint. This is a dangerous practice because the machinist can be pulled into the revolving massive equipment and injured. Moreover, as the gauge is repeatedly used, it becomes progressively worn and inaccurate, and ultimately must be replaced.
Accordingly, it would be desirable to have a means by which the threaded box and pin ends of a joint can be rapidly and efficiently gauged. It would be desirable if such a gauge did not have to be threadedly made up respective to the box and pin ends, and which did not significantly wear with use, and which included means indicating the precise additional material to be removed so as to reduce working time and enhance safety, thereby providing a low cost thread gauge. Such a desirable tool is the subject of this invention.